Towards an integrated approach to study SNPs and expression of candidate genes associated with milk protein biosynthesis.

MilkProtChip is oligonucleotide microarray allowing bovine genotyping based on single nucleotide polymorphisms (SNPs) in genes influencing milk protein biosynthesis. A total of 71 SNPs in 42 genes were selected as associated with milk protein biosynthesis. Genotyping of about 300 animals of Polish Black-and-White cattle showed that SNPs in acyl-CoA: 1,2-diacylglycerol O-transferase (DGAT1), lactoferrin (LTF), casein kappa (CSN3) and growth hormone receptor (GHR) genes were associated with several milk performance traits. Analysis of correlations between SNPs and milk production traits showed that SNPs in single genes rarely affect the investigated traits. Only 4 of 42 investigated single SNPs had impact on milk production traits while 22 combinations of paired SNPs in these genes had impact. Positive effect SNP combinations in two genes can be a result of additive effect on these SNPs on the same traits or effect of genes interaction. The MilkBovExp chip representing 90 genes encoding transcription factors expressed in the bovine mammary gland and/or involved in mammary gland signaling pathways was designed for further investigation of impact of gene expression and/or its encoded products on milk traits performance.